Tensor Modes: CAMB vs. CMBFast

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
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Tom Montroy
Posts: 1
Joined: April 12 2005
Affiliation: Case Western Reserve University

Tensor Modes: CAMB vs. CMBFast

Post by Tom Montroy » April 12 2005

hi all,

I've been comparing model power spectrum from Camb (Nov04 vers) and CMBFast 4.5.1. From what appear to be similar inputs, for the same T/S I get factor of 1.5-2 differences in the tensor power spectrum between Camb and CMBFast at l<100 (with CAMB being lower).

Odds are that I'm doing something wrong. Does anyone have CAMB and CMBFast parameter files for the same cosmology that give identical results for tensor modes. I'd like to compare those with mine to see what I might be doing wrong.

thanks,

Tom Montroy

Antony Lewis
Posts: 1547
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: Tensor Modes: CAMB vs. CMBFast

Post by Antony Lewis » April 12 2005

Usually just a problem of normalization. Make sure you use CMBFAST with UNNORM option, and note that CAMB does not use the quadrupole ratio rather the primordial power spectrum ratio. Also by default CAMB outputs in \mu K^2.

Here are sets of inputs that to generate tensor-only spectra that give reasonably consistent results:

CMBFAST

Code: Select all

0
2000 4000
1
-1
0.05 0.25 0.7 0
68 2.726 0.24 3.04 0 10.75
1
2
15 1
2
1 0 0
cmbfast_tensor.dat
jl.dat
CAMB:

Code: Select all

get_scalar_cls = F
get_vector_cls =  F
get_tensor_cls = T
COBE_normalize = F
CMB_outputscale = 1
get_transfer = F
do_nonlinear = 0
l_max_tensor = 2000
k_eta_max_tensor = 4000
w = -1
cs2_lam =    1.00000000000000
hubble = 70
use_physical = F
omega_baryon = 0.05
omega_cdm = 0.25
omega_lambda = 0.7
omega_neutrino = 0
temp_cmb = 2.726
helium_fraction = 0.24
massless_neutrinos = 3.04
massive_neutrinos = 0
reionization = T
re_use_optical_depth = F
re_redshift = 15
re_ionization_frac = 1
recombination =            1
initial_power_num = 1
scalar_spectral_index&#40;1&#41; = 1
scalar_nrun&#40;1&#41; =   0.000000000000000E+000
tensor_spectral_index&#40;1&#41; = 0
initial_ratio&#40;1&#41; = 1
scalar_amp&#40;1&#41; = 1
tensor_output_file = CAMB_tensor.dat
accurate_polarization = T
accurate_reionization = T
accurate_BB = T
do_late_rad_trunction =  T
do_tensor_neutrinos = T
feedback_level = 2
massive_nu_approx = 1
number_of_threads = 0
accuracy_boost = 1
l_accuracy_boost = 1
l_sample_boost = 1

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